Osmium, deposition

Ruthenium and osmium depositions on platinum are of special interest with reference to methanol anodic oxidation on fuel cells and were first reported in the early 1960s [116,117], Among the different methods of deposition of ruthenium or osmium on platinum [116-121], the spontaneous deposition method is attractive because of its simplicity and the fast achievement of a surface concentration plateau (reached in seconds) [26,122,123]. Contrary to the reversible behavior of the electrochemically deposited ruthenium on noble metal substrates, the films formed by spontaneous deposition normally do not dissolve easily from the metal surface. They are very stable and normally change to stable hydroxides and oxides when the electrode potential is increased. 

The study of a sublayer or a monolayer of ruthenium or osmium on platinum allows for an understanding of the role of the surface composition in the electrocatalysis of organic fuels, such as methanol oxidation. Interesting papers about ruthenium and osmium deposition on platinum single crystals and pc surfaces have been published [26,124—126],... 

In our proposed application, solutions of osmarins are to be injected directly into the synovial spaces of arthritic joints. The aim is to provide osmium deposits similar to those which Bousinna, et. al., (3) have suggested may be beneficial, while at the same time, avoiding the damage that accompanies OsO injections. 

Platinum occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural mountains, of Columbia, and of certain western American states. Sperrylite, occurring with the nickel-bearing deposits of Sudbury, Ontario, is the source of a considerable amount of metal. 

Other Metals. Ruthenium, the least expensive of the platinum group, is the second best electrical conductor, has the hardest deposit, and has a high melting point. A general purpose bath uses 5.3 g/L of mthenium as the sulfamate salt with 8 g/L sulfamic acid, and is operated at 25—60°C with a pH of 1—2. Osmium has been plated from acid chloride solutions (130) and iridium from bromide solutions, but there are no known appHcations for these baths. 

The distinction between the first member of the group and the two heavier members, which was seen to be so sharp in the early groups of transition metals, is much less obvious here. The only unsubstituted, discrete oxoanions of the heavier pair of metals are the tetrahedral [Ru 04] and [Ru 04]. This behaviour is akin to that of iron or, even more, to that of manganese, whereas in the osmium analogues the metal always increases its coordination number by the attachment of extra OH ions. If RUO4 is dissolved in cold dilute KOH, or aqueous K2RUO4 is oxidized by chlorine, virtually black crystals of K[Ru 04] ( permthenate ) are deposited. These are unstable unless dried and are reduced by water, especially if alkaline, to the orange... 

Ruthenium, iridium and osmium Baths based on the complex anion (NRu2Clg(H20)2) are best for ruthenium electrodeposition. Being strongly acid, however, they attack the Ni-Fe or Co-Fe-V alloys used in reed switches. Reacting the complex with oxalic acid gives a solution from which ruthenium can be deposited at neutral pH. To maintain stability, it is necessary to operate the bath with an ion-selective membrane between the electrodes . 

Iridium and osmium are rarely deposited. A new osmium bath is based on the hexachloroosmate ion . Procedures were outlined for depositing osmium on targets for nuclear reactions . 

A particularly interesting case is that of the platinum metal group which, in addition to platinum (Pt), comprises ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), and palladium (Pd). These carbonyl halides are usually the most practical precursors for metal deposition because of their high volatility at low temperature. Indeed two of them, palladium and platinum, do not form carbonyls but only carbonyl halides. So does gold. 

Iridium i s the most corrosion and oxidation resi stant metal and the densest element after osmium. It i s hard and brittle and as such it i s difficult to machine or form. Thi s limitati on has spurred the devel opment of vapor deposition. 

Just a few years after the discovery of the deposition and electroactivity of Prussian blue, other metal hexacyanoferrates were deposited on various electrode surfaces. However, except for ruthenium and osmium, the electroplating of the metal or its anodizing was required for the deposition of nickel [14], copper [15,16], and silver [9] hexacyanoferrates. Later studies have shown the possibilities of the synthesis of nickel, cobalt, indium hexacyanoferrates similar to the deposition of Prussian blue [17-19], as well as palladium [20-22], zinc [23, 24], lanthanum [25-27], vanadium [28], silver [29], and thallium [30] hexacyanoferrates. 

Fig. 3. (A) Stereo pair of starfish sperm chromatin fibers stained with osmium ammine-B. Bracket indicates the fine deposition of stain on nucleosomes and linker DNA. Arrowheads indicate where fibers enter and exit the plane of the section, and asterisks indicate sharp bends in the fibre axis. (B) Stereo pair of a reconstructed volume of a starfish sperm head by EM tomography. Axes of some fibers have been marked. Arrowhead indicates where individual fibers cannot be distinguished (from Ref. [27]). Scale bar 100 nm.

Platinum is the main metal in the platinum group, which consists of metals in both period 5 and period 6. They are ruthenium (Ru), rhodium (Ro), and palladium (Pd) in period 5 and osmium (Os), iridium (Ir), and platinum (Pt) in period 6. All six of these metals share some of the same physical and chemical properties. Also, the other metals in the group are usually found in platinum ore deposits. 

Figure 11.28 shows the rhenium and osmium isotopic compositions of black shales and sulfide ores from the Yukon Territory (Horan et al., 1994). The black shale and sulfide layers are approximately isochronous. The superimposed reference isochrons bracket the depositional age of the enclosing shales. One reference line represents the minimum age (367 Ma) with an initial ( Os/ Os)q ratio of one, consistent with the mantle isotopic composition at that age (see later). The other reference isochron is drawn for a maximum age of 380 Ma, with ( 870s/ 860s)o = 12 (the maximum value measured in terrigenous sediments). Further examples of application of Re-Os dating of sediments can be found in Ravizza and Turekian (1989). 

The orange-colored solution, containing, among other things, potassium ruthenate, was treated with nitric acid, whereupon a black precipitate of osmium dioxide containing from fifteen to twenty per cent of ruthenium oxide was thrown down as a velvety deposit. Klaus distilled this with aqua regia, taking care to condense the osmium tetroxide. The residue... 

Diammino-osmo-hydroxide, [OsO(NH3)2](OH)2, is prepared from osmium tetroxide and excess of concentrated aqueous ammonia. The yellow liquid obtained is heated in a closed vessel at 50° C. till it becomes dark brown in colour and a black powder is deposited. It is then exposed to the atmosphere and evaporated at low temperature, when a blackish-brown powder is deposited. The dry powder decomposes explosively on heating, with evolution of nitrogen. It dissolves in acids yielding the corresponding salts, and from these the base may be precipitated on the addition of aqueous alkali hydroxide. On boiling with a solution of alkali, however, the base is decomposed, ammonia is liberated, and a precipitate of osmium dioxide remains.1... 

Esser and Turekian (1988) estimated an accretion rate of extraterrestrial particles in ocean bottom and in varved glacial lake deposit on the basis of osmium isotope systematics and concluded a maximum accretion rate of between 4.9 x 104 and 5.6 x 104 tons/a. The discrepancy between this estimate and those derived from helium can easily be attributed to the difference in the size of the cosmic dust particles under consideration. Cosmic dusts of greater than a few ten micrometers may not be important in the helium inventory of sediments because the larger grains are likely to lose helium due to atmospheric impact heating (e.g., Brownlee, 1985). Stuart et al. (1999) concluded from studies on Antarctic micrometeorites that 50- to 1 OO-qm micrometeorites may contribute about 5% of the total flux of extraterrestrial 3He to terrestrial sediments. Therefore, the helium-based estimate deals only with these smaller particles. 

One group of NADH oxidants, which does not fit the proposed reaction scheme in Fig. 2.4 are the metal complexes. Examples of this type include nickel hexacyanoferrate deposited on porous nickel electrodes [29], gold electrodes modified with cobalt hexacyanoferrate films [30] and adsorbed l,10-phenanthroline-5,6-dione complexes of ruthenium and osmium [31]. It is unclear how these systems work and no mechanism has been proposed to date. It may be worth noting that dihydronicotinamide groups have been shown to reduce aldehydes in a non-enzymatic reaction when the reaction is catalysed by zinc, a metal ion [15]. In a reaction between 1,10-phenanthroline-2-carboxaldehyde and N-propyl-l,4-dihydronicotinamide, no reaction was seen in the absence of zinc but when added to the system, the aldehyde was reduced and the nicotinamide was oxidised. This implies that either coordination to, or close proximity of, the metal ion activates... 

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